1. Field of the Invention
Embodiments described herein relate generally to a multi charged particle beam writing apparatus and a multi charged particle beam writing method, and for example, a method for making a plurality of irradiation positions by multi-beams with high precision.
2. Related Art
A lithography technique that is charge in the progress of refinement of a semiconductor device is a very important process to generate a unique pattern in a semiconductor fabricating process. In recent years, with high integration of LSI, a line width of a circuit required for the semiconductor device has been refined every year. Herein, an electron ray (electron beam) writing technique intrinsically has excellent resolution and a pattern is written on a wafer and the like by using an electron ray.
For example, a writing apparatus using multi-beams is used. As compared with a case of writing the pattern by using one electron beam, since a lot of beams may be irradiated once by using the multi-beams, throughput may be significantly improved. In the multi-beam type writing apparatus, for example, an electron beam emitted from an electron gun passes through a mask having a plurality of holes to form the multi-beams, the multi-beams are blanking-controlled, and each beam which is not shielded is reduced by using an optical system, and is deflected by using a deflector to be irradiated to a desired point on a target object (see Published Unexamined Japanese Patent Application No. 2006-261342 (JP-A-2006-261342), for example).
In the multi-beam type writing apparatus, the plurality of beams are irradiated at a time and irradiation positions of the plurality of beams are required to be adjusted with high precision. For example, with respect to the written pattern, the reduction rate of a lens of the optical system is adjusted, such that it is considered to adjust the size by adjusting the size of each beam. However, when a lens condition is changed, a phenomenon in which the pattern rotates or a phenomenon in which field deformation is changed occurs. As a result, it is difficult to set the lens condition to an optimized state together with a lot of other parameters required for the optical system so that the size precision becomes high precision. In the case of mechanical rotation fitting, adjustment of an accurate rotational position of an nm order is required, which is not realistic. In the case of field deformation, first, the field is deformed in the optical system, in principle. As fabrication precision, in order to adjust the fabrication precision to precision of, for example, nm or less (for example, 0.1 nm), a significantly close design is required, which is not also realistic. In designing the optical system, even though the optical system may be designed with high precision, setting ranges of other design parameters are limited. As a result, when field deformation intends to be modified, optimization of these other conditions (for example, resolution performance, focal depth, and the like) may be interfered. When equalization of a magnetic field intends to be promoted in order to reduce deformation, for example, a huge lens barrel is required. A lot of complicated correction mechanisms are required in order to reduce deformation and an excessive burden is applied to the apparatus. After the writing apparatus is manufactured, adjustment to an actual apparatus is required, but although deformation intends to be modified, parameters of writing are complicatedly related to each other, and thus a parameter for modifying the deformation is not an independent variable. Therefore, optimization is difficult or enormous amount of time is required although the optimization may be achieved.
As described above, in the multi-beam type writing apparatus, the plurality of beams are irradiated at a time and irradiation positions of the plurality of beams are required to be adjusted with high precision. In the multi-beam type, beams that pass through different molding holes are partially overlapped and connected, and a pattern having a desired figure shape is formed. When the beam is deviated from a desired irradiation position due to deformation of the optical system and the like, an overlap amount among the irradiation beams is deviated and it is difficult to write the pattern with high precision.